Route xAI OAuth through device-code sign-in so remote and headless hosts do not need a localhost callback. Preserve the legacy manual `xai-device-code` auth choice/method as a compatibility alias to the same device-code flow.
Also migrate stale xAI token endpoints on refresh and fail fast on structured refresh errors while keeping retries scoped to detected HTML/Cloudflare challenge responses.
Verification:
- `node scripts/run-vitest.mjs extensions/xai/index.test.ts extensions/xai/xai-oauth.test.ts`
- `node scripts/run-vitest.mjs src/cli/models-cli.test.ts -t 'maps --device-code'`
- `node scripts/run-vitest.mjs src/commands/auth-choice.test.ts -t 'removed provider auth choice'`
- Crabbox local-container live smoke on exact head `fef3cb24afb01cd1f69cf04ef67ed11d71dfadb3`: xAI discovery and device authorization returned 200.
- `$autoreview` after the live smoke: clean.
Co-authored-by: Jaaneek <Jaaneek@users.noreply.github.com>
Co-authored-by: fuller-stack-dev <263060202+fuller-stack-dev@users.noreply.github.com>
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